1. Field of the Invention
The present invention relates to a device for transferring plate-like objects such as semiconductor wafers.
2. Description of the Related Art
The semiconductor wafer processing apparatuses have a carrier mechanism or device for transferring or carrying wafers, which will be loaded into and unloaded from a process section, into a housing section such as the cassette. One of these wafer processing apparatuses which use this carrier mechanism is the heat processing apparatus. This heat processing apparatus is intended to oxidize, diffuse and anneal the wafer or film-form on it. Plural sheets of semiconductor wafers are transferred from the cassette into a boat, which will be loaded into a heat processing tube, in the heat processing apparatus, or these semiconductor wafers which have been unloaded from the heat processing tube are transferred from the boat into the cassette in it.
As shown in FIG. 1, the carrier device is arranged in a load/unload section of the heat processing apparatus to transfer semiconductor wafers between the cassette and the boat. It is intended to increase throughput in the course of making semiconductor devices, and it can carry the wafers all at once. The carrier device has an arm mechanism 10 rotatable, movable up and down and reciprocatable. This arm mechanism 10 has a wafer-mounted section, on which five sheets of wafers can be mounted, at the front end of an arm. It can transfer five sheets of wafers all at once between the cassette 12 and the boat 14.
On the other hand, it is sometimes needed that only one sheet of monitor or dummy wafer is transferred into the boat 14. In addition to the above-mentioned plural wafers carrying arm mechanism, therefore, a one wafer carrying arm mechanism is needed.
As shown in FIG. 3, the single and plural sheets carrying arm mechanisms 22 and 20 are arranged one upon the other in the conventional carrier device, and the single sheet carrying arm mechanism 22 is driven independently of the plural sheets one 20. Five sheets carrying arms 20A are arranged at a same pitch interval but the single sheet carrying arm 22A has no pitch interval relative to the plural sheets ones 20A. In short, the interval of the single sheet carrying arm 22A relative to the plural sheets ones 20A is larger than the pitch interval at which the plural sheets carrying arms 20A are arranged one another. This is intended to prevent both of the arms 20A and 22A from interfering with each other when they are being moved. Therefore, the space the conventional carrier device occupies is large and the device itself is also large in size.
Further, both mechanisms 20 and 22 are driven independently of the other. This makes it necessary to independently position each of them. Teaching procedure which is carried out in a drive section to position each of them becomes complicated accordingly, and positioning error thus obtained may be large. Both of the mechanisms 20 and 22 are also assembled independently of the other. This increases the number of parts used and the number of assembling steps for them. Cost for each mechanism, therefore, becomes high.